1. Field of the Invention
This invention relates to a hook switch used mainly in a telephone set to switch over, for example, from the signal receiving circuit to the outgoing and speaking circuit and vice versa.
2. Description of the Prior Art
A conventional example of such a hook switch as stated above is shown in FIG. 5. This hook switch is composed of a body 100 and an actuator 200. On the body 100 are disposed plural contact pieces, for example as illustrated, a first contact piece 110 is sandwitched between a second contact piece 120 and a third contact piece 130 from both upper and lower sides with interspaces. Terminals 111, 121 and 131 extending from these contact pieces 110, 120, 130 are projected from the front edge of a bottom wall of the body 100. The front end part of the first contact piece 110 is elastically in contact with the lower surface of an engaging part 101 formed on the rear end part of the body 100. The actuator 200 is supported rotatably on a protrusion 102 installed on the body at its middle part in the longitudinal direction, and a first fitting part 201 located on the rear end corresponds to the second contact piece 120 and a second fitting part 202 corresponds to the third contact piece 130. The actuator 200 is here thrust downward at its rear end part by a spring 300.
In this hook switch, when a handset of a telephone set, for example, is lifted from the main body of the telephone set, the actuator 200 is thrust by the spring 300 to be in the state shown in the drawing. In this state, the second contact piece 120 is pushed in by the first fitting part 201 to come into contact with the first contact piece 110, while the third contact piece 130 is pushed in by the second fitting part 202 and moved away from the first contact piece 110. When the handset is, for example, placed on the telephone set and the front end part of the actuator 200 is pivoted downward about a support point P formed on the protrusion 102, the first fitting part 201 is moved upward along with the movement of the rear end of the actuator 200 in the upper direction, so that the second contact piece 120 is displaced upward and is parted from the first contact piece 110 as indicated by the virtual line. At the same time, the second fitting part 202 of the actuator 200 is moved upward and the third contact piece 130 is displaced upward as indicated by the virtual line to come into contact with the first contact piece 110.
In such a hook switch, for example, the timing of the second contact piece 120 to contact or part form the first contact piece 110 and the contacting pressure between them are related to the moving width A.sub.1 of the first fitting part 201 in the vertical direction around the support point P, and this moving width A.sub.1 is, in turn, related to the interspace L.sub.1 between the first fitting part 201 and the support point P on/and to the height of the first fitting part 201 (the protruding width from the inner surface of the actuator 200). Likewise, the contacting and parting timings of the third contact piece 130 with regard to the first contact piece 110 and their contacting pressure are related to the interspace L.sub.2 between the support point P and the second fitting part 202 or/and to the height of the second fitting part 202.
In a different type of hook switch in which plural second contact pieces 120 correspond to plural first contact pieces 110, respectively as shown in FIG. 6, if it is necessary to slightly shift these contacting and parting timings of the second contact pieces 120, with regard to the first contact pieces 110, it was conventionally designed to produce step differences at the positions F.sub.1, F.sub.2, F.sub.3 on the first fitting part 201 corresponding to the second contact pieces 120, and to set the step differences to be switched for the contacting and parting timings. In a further different hook switch in which plural third contact pieces 130, correspond respectively to plural first contact pieces 110, step differences are formed at the positions of the second fitting part 202 confronting the third contact pieces 130, and the step differences are set precisely to be switched for the contacting and parting timings.
In the conventional hook switch, however, in order to obtain appropriate contacting and parting timings, it was necessary to set the interspaces L.sub.1 and L.sub.2 and the height of the first fitting part 201 and the second fitting part 202 precisely in relation to the moving widths A.sub.1 and A.sub.2 of the first contact piece 110 and the third contact piece 130, and moreover to set the step differences mounted on the first fitting part 201 and the second fitting part 202 precisely. It is very troublesome technically from a design point of view to set them precisely, and the hook switch thus became too expensive. In addition, in variously designed telephone sets, diversified shapes of actuators 200 are required. But in the conventional hook switch in which the first fitting part 201 and the second fitting part 202, that control the contacting and parting timings, are mounted on the actuator 200 itself, it was impossible to fully meet such demands for diversification because of the difficulty in design and technique as stated above.
On the other hand, in the conventional hook switch, when the number of contact pieces increases, the elasticity of these contact pieces significantly influences the operating effort of the actuator 200, so that a greater force is required to operate the actuator. Hence, these was a limit to making a multipolar system by increasing the number of contact pieces, which hindered its application into the apparatus such as telephone sets having a lot of control circuits.